Porous polymeric particles have been prepared and used for many different purposes. For example, porous particles have been described for use in chromatographic columns, ion exchange and adsorption resins, drug delivery devices, cosmetic formulations, papers, and paints. The methods for generating pores in polymeric particles are well known in the field of polymer science. However, each particular porous particle often requires unique methods for their manufacture. Some methods of manufacture produce large particles without any control of the pore size while other manufacturing methods control the pore size without controlling the overall particle size.
Marker material can be included in porous particles so that the particles can be detected for a specific purpose. For example, U.S. Patent Application Publications 2008/0176157 (Nair et al.) and 2010/0021838 (Putnam et al.) and U.S. Pat. No. 7,754,409 (Nair et al.) describe porous particles and a method for their manufacture, which porous particles are designed to be toner particles for use in electrophotography. Such porous particles (“toners”) can be prepared using a multiple emulsion process in combination with a suspension process (such as “evaporative limited coalescence”, ELC) in a reproducible manner and with a narrow particle size distribution.
Toner particles having a luminescent material that includes quantum dots are described in EP 2,025,525 (Wosnick et al.) and can be used to form detectable markings on substrates. These toner particles can also include colorants or other detectable components.
U.S. Pat. No. 7,887,984 (Nair et al.) describes porous toner particles comprising a continuous binder polymer phase and a second phase of a hydrocolloid in discrete pores. These porous toner particles are prepared using limited coalescence techniques.
U.S. Pat. No. 8,110,628 (Nair et al.) describes the preparation of porous particles having first and second discrete pores in which are incorporated detectably different marker materials. Such porous particles are prepared using multiple water-in-oil emulsions and various discrete pore stabilizing hydrocolloids.
While the noted methods and porous particles provide significant advances in the art, there is a need for a way to prepare porous particles that can be free of detectable markers, but which have sets of pores having different averages sizes, for example as bimodal or multi-modal size distribution.
Porous polymeric particles of controlled size are useful in diverse applications such as physical spacers, gaseous absorbers, optical barriers and diffusers, permeable barriers, electrophotographic toners, lubricants, dessicants, and dispersive media. Porous polymeric particles having discrete pores of controlled size are likewise of technological importance to these and other applications where the precise control of particle density, optical scatter, particle modulus, or elasticity or internal porous surface area is advantageous. There is a need to find a way to prepare such porous polymeric particles in a reproducible manner.